For example, a centrifugal chiller has been employed for realizing district cooling/heating, cooling/heating for a semiconductor factory or the like, and so forth. FIG. 8 shows a configuration diagram of a heat source system employing a conventional centrifugal chiller. As shown in FIG. 8, a centrifugal chiller 70 cools chilled water (heating medium) supplied thereto from an external heat load 71, such as an air conditioner, a fan coil, or the like, to a predetermined temperature and supplies the cooled chilled water to the external load 71. A chilled-water pump 72 that feeds the chilled water is installed upstream of the centrifugal chiller 70 with respect to the flow of the chilled water. In addition, a chilled-water flow rate meter 73 that measures the flow rate of chilled water flowing out of the chilled-water pump 72 is provided downstream of the chilled-water pump 72. The output from this chilled-water flow rate meter 73 is sent to a control device (not shown) that controls the centrifugal chiller 70, and the centrifugal chiller 70 is controlled by using this chilled-water flow rate as one of the control parameters.